Liquid ejection apparatus

ABSTRACT

The present invention provides a liquid ejection apparatus capable of precisely controlling a flow rate of liquid in a flow-path. The liquid ejection apparatus is equipped with: an ejection head that is provided with a feed port and a discharge port, and that ejects fed liquid; a feed flow-path that feeds liquid to the feed port; a discharge flow-path that discharges liquid from the discharge port; at least one of the feed flow-path and/or the discharge flow-path equipped with a main pump that pumps a constant flow rate of liquid in the flow-path, a sub pump provided in parallel to the main pump and that pumps liquid in the flow-path, and a detector unit that detects liquid pressure in the flow-path; and a control unit that controls the flow rate of liquid pumped by the sub pump such that the pressure detected achieves a predetermined pressure.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority under 35 USC 119 from Japanese Patent Application No. 2008-251032 filed on Sep. 29, 2008, the disclosure of which is incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid ejection apparatus. In particular the present invention relates to a liquid ejection apparatus using pumps.

2. Description of the Related Art

A technique is known in ink-jet-type liquid ejection apparatuses in which a biasing unit such as a pump is used to circulate liquid in a flow-path in order to prevent drying out of the nozzle meniscus portion of a printing head. For example, an inkjet apparatus control method is described in Japanese Patent Application Laid-Open (JP-A) No. 2007-313884. In this inkjet apparatus, a first pressure source and a second pressure source are respectively disposed at the inlet side and the outlet side of a head. Further, in the inkjet apparatus control method, as a technique for adjusting pressure in an ink tank that is a pressure source, the air pressure at the top of the ink tank is controlled while maintaining a liquid surface height in the ink tank by using a liquid pump, and pressure is also controlled by changing the placement height of the ink tank.

A technique is described in JP-A No. 2006-175651 relating to ink circulation for a long head. In this technique, a pressure pump for a head is in direct communication with the head, and the rotation speed of the pump is determined so that the head achieves a specific pressure.

However, when the technique described in JP-A No. 2007-313884 is applied to a system that circulates and consumes large volumes of ink, such as a line head, the speed of control may not be quick enough. In addition, in the method of controlling pressure by liquid surface height, there is air present in the ink tank above the ink. Accordingly, there are occurrences of air bubbles flowing into the head and air dissolving in the ink etc., causing poor ejection.

Further, JP-A No. 2006-175651 does not describe a technique for precisely maintaining a constant pressure.

Accordingly, precise control of the flow rate of a liquid in a flow-path is difficult with existing techniques.

SUMMARY OF THE INVENTION

The present exemplary embodiment provides a liquid ejection apparatus capable of precisely controlling the flow rate of liquid within a flow-path.

A first aspect of the present invention is a liquid ejection apparatus including: an ejection head including a feed port for feeding liquid in and a discharge port for discharging liquid out, and that ejects fed liquid; a feed flow-path that feeds liquid to the feed port; and a discharge flow-path that discharges liquid from the discharge port; wherein at least one of the feed flow-path or the discharge flow-path includes, a main pump that pumps a liquid at a constant flow rate in the at least one of the feed flow-path or the discharge flow-path, a sub pump provided in parallel to the main pump and that pumps liquid in the at least one of the feed flow-path or the discharge flow-path, and a detector unit that detects pressure of liquid in the at least one of the feed flow-path or the discharge flow-path; and wherein the liquid ejection apparatus further includes, a control unit that controls the flow rate of liquid pumped by the sub pump such that the liquid pressure detected in the at least one of the feed flow-path or the discharge flow-path achieves a predetermined pressure.

In the first aspect of the present invention, the feed port for feeding liquid in and the discharge port for discharging liquid out are provided to the ejection head. The ejection head also ejects fed liquid. Further, in the first aspect, at least one of the feed flow-path that feeds liquid to the feed port and/or the discharge flow-path that discharges liquid from the discharge port is equipped with the main pump, the sub pump, and the detector unit. The main pump pumps a constant flow rate of liquid in the flow-path. The sub pump is provided in parallel to the main pump and pumps liquid in the flow-path. The detector unit detects pressure of liquid in the flow-path. The control unit controls the flow rate of liquid pumped by the sub pump such that the liquid pressure detected by the detector unit in the flow-path reaches a predetermined pressure. Accordingly, the first aspect of the present invention provides a liquid ejection apparatus that can precisely control the flow rate of liquid in the flow-path. In particular, the first aspect of the present invention can further precisely control the liquid flow rate in the flow-path, if both the feed flow-path and the discharge flow-path are equipped with a sub pump and a detector unit, and are configured so as to perform control as described above.

In a second aspect of the present invention, in the above-described aspect, each of the feed flow-path and the discharge flow-path may respectively include the main pump; and a common drive source may be used for driving the main pump.

In the second aspect of the present invention, each of the feed flow-path and the discharge flow-path respectively includes main pumps that include a common drive source used therefor. Accordingly, the second aspect of the present invention can provide a lower cost liquid ejection apparatus in comparison to cases where separate drive sources are provided for each main pump.

Accordingly, the present invention can provide a liquid ejection apparatus capable of precisely controlling the flow rate of liquid in a flow-path.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein:

FIG. 1 is a drawing showing a configuration of a liquid ejection apparatus according to an exemplary embodiment;

FIG. 2 is a diagram showing the electrical configuration of a liquid ejection apparatus according to an exemplary embodiment;

FIG. 3 is a flow chart showing pressure control process flow;

FIG. 4 is a flow chart showing pressure control process flow of a feed flow-path; and

FIG. 5 is a flow chart showing pressure control process flow of a discharge flow-path.

DETAILED DESCRIPTION OF THE INVENTION

An exemplary embodiment of the present invention will be described in detail below with reference to the drawings. It should be noted that in the explanation below, a liquid is described as ink. An inkjet recording device is given as an example of a liquid ejection apparatus.

FIG. 1 shows a configuration of a liquid ejection apparatus according to the present exemplary embodiment. As shown in FIG. 1, the liquid ejection apparatus is configured to include pumps, tanks, valves, ejection heads (referred to below as heads), and a degas device. The degas device indirectly reduces air bubbles contained in the ink.

A feed port for ink feed and a discharge port for ink discharge are provided to the head. The head ejects ink that has been fed in. There are two heads depicted in FIG. 1. However, the number of heads may also be one, or three or more.

In such cases the number of flow-paths connecting each head to a feed tank 28 and a recovery tank 30 are increased according to the number of heads. The number of valves provided on the flow-paths connecting the heads to the feed tank 28 and the recovery tank 30 are also increased along with the increase in the number of flow-paths.

In the configuration shown in FIG. 1, the flow-path from a buffer tank 20, and extending through a degas device 24, a buffer tank 26, a pump 18A (main pump), a pump 18B (sub pump), the feed tank 28, to the heads 10A, 10B, is a feed flow-path. The flow-path from the heads 10A, 10B, and extending through the recovery tank 30, pumps 18C, 18D, to a buffer tank 20, is a discharge flow-path.

Explanation will now be given of each part of the configuration. The main tank 22 is an ink cartridge, which is removably mounted in the liquid ejection apparatus. The main tank 22 and the buffer tank 20 are connected together by a flow-path. Note that, ink flows from the main tank 22 to the buffer tank 20.

The buffer tank 20 and the degas device 24 are connected together by a flow-path. The degas device 24, by reducing the pressure of the ink with a vacuum pump or the like, discharges air dissolved in the liquid through a gas permeable membrane (generally a membrane of hollow fiber form). The degas device 24 thereby indirectly reduces air bubbles.

The ink that has flowed from the buffer tank 20 is deaerated by the degas device 24. The degas device 24 and the buffer tank 26 are also connected together by a flow-path. The ink that has been degased by the degas device 24 flows into the buffer tank 26.

The buffer tank 26 and the feed tank 28 are connected together by a flow-path via the pumps 18A, 18B.

As shown in FIG. 1, the pump 18A is provided in the flow-path that connects the feed ports of the heads 10A, 10B to the discharge ports of the heads 10A, 10B. The pump 18A pumps a constant flow rate of liquid in the flow-path. The pump 18B is provided in parallel to the pump 18A and pumps liquid in the flow-path.

The feed tank 28 temporarily accumulates ink that is to be feed to the heads 10A, 10B. A pressure sensor 14 is provided to the feed tank 28, and detects the pressure of ink in the feed tank 28 (namely, the pressure of the ink within the feed flow-path). The feed tank 28 is connected by flow-paths to the head 10A and to the head 10B, via a valve 12A and a valve 12B, respectively.

Valves 12A, 12B, 12C, 12D are, for example, electromagnetic valves. The valves 12A, 12B, 12C, 12D stop the feed of ink to each of the heads 10A, 10B.

The head 10A and the head 10B are each formed with a flow-path communicating their respective feed ports with respective discharge ports, and the heads 10A, 10B eject ink that has been fed form the flow-paths.

The head 10A and the head 10B are connected to the recovery tank 30 by flow-paths including the valves 12C, 12D, respectively. The recovery tank 30 temporarily accumulates ink recovered from the heads 10A, 10B.

A pressure sensor 16 is provided to the recovery tank 30 for detecting the pressure of ink in the recovery tank 30 (namely, the pressure of ink in the discharge flow-path). The recovery tank 30 and the buffer tank 20 are connected together by a flow-path via the pump 18C (main pump) and the pump 18D (sub pump).

As shown in FIG. 1, on the discharge path, which is the other flow-path on which the pumps 18A, 18B and the pressure sensor 14 are not provided, there is further provided the pump 18C that pumps liquid with a constant drive force in the discharge flow-path, the pump 18D is provided in parallel to the pump 18C and pumps liquid in the discharge flow-path, and a pressure sensor 16 is also provided for detecting the pressure of liquid in the discharge flow-path.

According to the configuration as explained above, the ink is fed from the buffer tank 20 to the heads 10A, 10B via the degas device and the others. In addition, ink discharged from the heads 10A, 10B flows back into the buffer tank 20.

It should be noted that, unidirectional pumps (diaphragm pumps, piston pumps or the like) may be used as the above described pumps 18A, 18C. Also a cheap pump with a long lifespan may be used as the above described pumps 18A, 18C. However, the pumps 18B, 18D are pumps which are capable of high precision control of liquid flow rate for relatively small flow rates in comparison to the pumps 18A, 18C. Further, it is preferable to use pumps (tube pumps, gear pumps or the like) that are capable of pumping liquid in forward and reverse directions for the pumps 18B, 18D.

The present exemplary embodiment employs one pump that pumps a larger flow rate of liquid with a constant flow rate, and employs a high precision pump for the other pump. Accordingly, the liquid ejection apparatus according to the present exemplary embodiment can precisely control the flow rate in the flow-path. In addition, the flexibility for selecting the pump increase in the liquid ejection apparatus of the present exemplary embodiment, by assigning roles to plural pumps, in comparison to a case where a single precision high-volume pump is employed. Accordingly, the present exemplary embodiment can provide a high precision ink ejection device that can be configured at low cost.

It should be noted that, in order to absorb rapid changes in ink pressure, a damper structure may be employed in the structure of the above described feed tank 28 and recovery tank 30.

Plural pumps may also be used to configure each of the respective pumps 18A to 18D. For example, the pumps 18A, 18C may be configured with plural pumps that pump a constant liquid flow through the flow-path. The pumps 18B, 18D may also be configured with plural pumps with which the liquid flow rate is controllable with a control unit.

Explanation will now be given of the electrical configuration of the liquid ejection apparatus, with reference to FIG. 2. As shown in FIG. 2, the electrical configuration of the liquid ejection apparatus includes a control unit 40, a valve control unit 42, a valve control unit 44, a motor drive switch 46, and a motor 48.

The control unit 40 is configured to include a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory) and others. A program for executing processes of a later described flow chart is stored in the RAM. Various data is stored in the RAM. The control unit 40 is connected to the valve control unit 44, the valve control unit 42, the pressure sensors 14, 16 and the motor drive switch 46. The control unit 40 performs overall control of the liquid ejection apparatus.

Specifically, the control unit 40 controls the drive force of the pump 18B to set the pressure of the liquid in the feed flow-path detected by the pressure sensor 14 at a predetermined pressure. The control unit 40 also controls the drive force of the pump 18D to set the pressure of liquid in the discharge flow-path detected by the pressure sensor 16 at a predetermined pressure.

Namely, the control unit 40 controls the pumps 18B, 18D to set the pressure of liquid in the flow-paths detected by the pressure sensors 14, 16 at respective predetermined pressures in each of the flow-paths.

The valve control unit 42 opens or closes each of the valves according to instructions from the control unit 40.

The valve control unit 44 controls the drive force of each of the pumps 18B, 18D according to instructions from the control unit 40, by changing the rotation speed of the motors driving the pumps 18B, 18D.

The motor drive switch 46 drives the motor 48 according to instructions from the control unit 40. The motor drive switch 46 drives the motor 48 by being switched ON, and stops driving the motor by being switched OFF. The present exemplary embodiment uses the common power source, which is the motor 48, to drive the pump 18A and the pump 18C. The present exemplary embodiment can thereby provide an even lower cost liquid ejection apparatus.

Explanation will now be given of the processes executed by the above described configuration, with reference to a flow chart. Note that, the processes of the flow chart described below are executed by the control unit 40.

Explanation will first be given of the pressure control processing according to the present exemplary embodiment, with reference to the flow chart of FIG. 3. First, at step 101, the control unit 40 acquires the pressure in the feed flow-path and the discharge flow-path. These pressures are acquired with the pressure sensors 14, 16.

Then, in the next step 102, the control unit 40 determines whether or not the pressure X of the feed flow-path is equivalent to that of a specific pressure Pl. The specific pressure P1 here, and a later described specific pressure P2, are pressures predetermined according to the material configuring the flow-paths, the components of the heads 10A, 10B, and others.

When determination at step 102 is affirmative, the control unit 40 performs the pressure control processing of the feed flow-path of step 104, described below, and the processing is ended.

However, when determination at step 102 is negative, the control unit 40 determines at step 103 whether or not the pressure Y of the discharge flow-path is equivalent to that of the specific pressure P2. If determination at step 103 is negative, then processing is ended here, since the pressures of the feed flow-path and the discharge flow-path are the predetermined pressures.

If determination at step 103 is affirmative then the control unit 40 performs the pressure control processing of the discharge flow-path of step 105, described below, and the processing is ended.

Note that, in the above described steps 102 and 103 determination is made as to whether or not there is a difference from the predetermined pressures. However, a range may be used for the predetermined pressures. Namely, if the acquired pressure is pressure Z, then determination may be made that Z is the predetermined pressure if p<Z<q (where p and q are pressures) is satisfied.

Explanation will now be given of the feed flow-path pressure control processing flow of above step 104, with reference to the flow chart of FIG. 4. First, at step 201, the control unit 40 determines whether or not the pressure X of the feed flow-path is greater than the specific pressure P1. When determination at step 201 is affirmative, at step 202 the control unit 40 instructs the valve control unit 44 to reduce the flow rate of liquid pumped by the pump 18B, and the processing is ended.

However, if determination at step 201 is negative, at step 203 the control unit 40 instructs the valve control unit 44 to increase the flow rate of liquid pumped by the pump 18B, and the processing is ended.

Explanation will now be given of the discharge flow-path pressure control processing of above step 105, with reference to the flow chart of FIG. 5. First, at step 301, the control unit 40 determines whether or not the pressure Y of the discharge flow-path is greater than the specific pressure P2. When determination at step 301 is affirmative, at step 302 the control unit 40 instructs the valve control unit 44 to reduce the flow rate of liquid pumped by the pump 18D, and the processing is ended.

However, if determination at step 301 is negative, at step 303 the control unit 40 instructs the valve control unit 44 to increase the flow rate of liquid pumped by the pump 18D, and the processing is ended.

In the pressure control processing of the feed flow-path and the discharge flow-path described above, when controlling the pressure of the flow-paths, the control unit 40 may perform control such that the flow of liquid is in the reverse direction rather than in the normal direction.

It should be noted that the process flows in each of the above flow charts are only examples thereof. Accordingly, changes to the processing sequence, addition of new steps, and deletion of redundant steps can obviously be made within a scope not departing from the spirit of the present invention. 

1. A liquid ejection apparatus comprising: an ejection head including a feed port for feeding liquid in and a discharge port for discharging liquid out, and that ejects fed liquid; a feed flow-path that feeds liquid to the feed port; and a discharge flow-path that discharges liquid from the discharge port; wherein at least one of the feed flow-path or the discharge flow-path includes, a main pump that pumps a liquid at a constant flow rate in the at least one of the feed flow-path or the discharge flow-path, a sub pump provided in parallel to the main pump and that pumps liquid in the at least one of the feed flow-path or the discharge flow-path, and a detector unit that detects pressure of liquid in the at least one of the feed flow-path or the discharge flow-path; and wherein the liquid ejection apparatus further comprises, a control unit that controls the flow rate of liquid pumped by the sub pump such that the liquid pressure detected in the at least one of the feed flow-path or the discharge flow-path achieves a predetermined pressure.
 2. The liquid ejection apparatus of claim 1, wherein: each of the feed flow-path and the discharge flow-path respectively include the main pump; and a common drive source is used for driving the main pump.
 3. A liquid ejection apparatus comprising: an ejection head including a feed port for feeding liquid in and a discharge port for discharging liquid out, and that ejects fed liquid; a feed flow-path that feeds liquid to the feed port; a discharge flow-path that discharges liquid from the discharge port; a main pump that pumps liquid at constant flow rate of liquid in the feed flow-path and in the discharge flow-path; a sub pump provided in parallel to the main pump and that pumps liquid in the feed flow-path and in the discharge flow-path; a first detector unit that detects liquid pressure in the feed flow-path; a second detector unit that detects liquid pressure in the discharge flow-path; and a control unit that controls the flow rate of liquid pumped by the sub pump such that the liquid pressures detected in the feed flow-path and in the discharge flow-path are within a predetermined pressure range.
 4. A method for controlling liquid ejection comprising: providing a liquid ejection control apparatus including, an ejection head that includes a feed port and a discharge port, and that ejects fed liquid, a feed flow-path that feeds liquid to the feed port, a discharge flow-path that discharges liquid from the discharge port, a main pump that pumps liquid at a constant flow rate in the feed flow-path and in the discharge flow-path, a sub pump provided in parallel to the main pump and that pumps liquid in the feed flow-path and in the discharge flow-path, a first detector unit that detects liquid pressure in the feed flow-path, a second detector unit that detects liquid pressure in the discharge flow-path, and a control unit that controls the flow rate of liquid pumped by the sub pump; controlling the flow rate of liquid pumped by the sub pump such that the liquid pressure detected by the first detector unit is within a predetermined pressure range; and controlling the flow rate of liquid pumped by the sub pump such that the liquid pressure detected by the second detector unit is within the predetermined pressure range. 